- New SubscriptionMatrixService for billing matrix generation
- Products grouped by product number with monthly aggregation
- Support for archived, draft, sent, booked, paid, unpaid invoices
- Fixed amount calculation with fallback logic (grossAmount, unitNetPrice)
- Status mapping based on invoice type (draft, invoiced, paid)
- Frontend tab on customer detail page with dynamic table rendering
- Fixed Blåhund customer economic number linking
